Modern vehicles are built to withstand the extremes of climate. Therefore, the human occupied portion of the vehicle tends to be a closed space which can be heated, or cooled, to an appropriate temperature for any human occupants. Being a closed space, however, requires that fresh air be provided to the interior.
Most vehicles, therefore, are provided with a fresh air intake conduit which allows fresh air from the outside to be passed into the interior of the vehicles. The majority of vehicles are equipped with a turbine fan blower air circulation system. This is widely used in both older and new vehicles. However, the so called "fresh air" from the outside is not fresh at all. For example, in a traffic jam, with a large number of vehicles producing fumes, the fresh air in-take of one vehicle may be simply taking in the fumes of a vehicle in front or at the side of it. This is especially true in urban and congested areas where overall air pollution is a serious problem.
In the past, this has been dealt with by the use of integrally built air filter conduit systems which are intended to be made part of the car. Ford's 1995 Mercury Mystique model has incorporated an occupant air filter, by redesigning the air circulation conduits to accept such a filter. In addition to Ford's design, for example, U.S. Pat. No. 5,192,346 to Kowalczyk shows a specialized conduit containing an air filter, which is inserted into the vehicle's air system between the fresh air inlet and the inside of the vehicle. However, this design is one that needs to be installed in the factory, and additionally requires a heater to keep the filter functioning correctly. Such a device is awkward, expensive to build and install, and generally impractical.